Computer systems typically include a processing unit, local memory, and several other functions. Some systems include the ability to incorporate additional functions through the use of an expansion bus. An expansion bus typically included one or more expansion connectors, each of which contains voltage, ground, data and control signals. An external circuit board, having the mating connector, can be inserted into the expansion bus connector. Since the expansion connector supplies all of the required power, data and control signals, the inserted circuit board is able to operate as if it were incorporated directly into the computer system. Each expansion connector on the computer system represents a slot into which an external circuit board may be inserted to augment the functionality of the computer system. Thus, these expansion connectors are sometimes referred to as “slots” or “expansion slots”
Various protocols are commonly used for these expansion busses. For example, PCI, an acronym for Peripheral Component Interconnect, has been used for many years to provide the ability to add additional functions to computer systems. The PCI protocol defines both the physical configuration of the expansion connector and the electrical specification of all of the signals used on that connector. In more recent years the PCI SIG has released an upgraded version of PCI called PCI Express, where the signaling protocol changed from a parallel to a serial implementation, as well as allowed for large bandwidth increases. PCI Express has released subsequent specification versions, also referred to as Gen 1, Gen 2 and more recently, Gen 3, respectively.
While computer systems may include one or more expansion slots, in some embodiments, there is a need for more expansion slots. In some scenarios, expansion boxes have been used. An expansion box is an accessory to the computer system, which includes a plurality of expansion slots. The Expansion box connects to the computer system via an expansion slot in the computer system. In some cases, the connection between the computer system and the expansion box is simply an expansion cable. In other words, a first circuit board, which contains only the mating connector and the expansion cable, is inserted into one of the expansion slots in the computer system. The far end of the expansion cable connects to a second circuit board, which is then plugged into the backplane of the expansion box.
While this mechanism has been used to provide additional expansion slots, as the speed of expansion busses has increased, the ability to make a low cost expansion box has decreased. For example, in some embodiments, the first circuit board described above, also includes active circuitry. For example, PCI Express switches chips, PCI Express repeater chips, or PCI Express retimer chips which buffer the PCI signals from the computer system to improve their signal integrity, have been used. While effective, this approach increases the cost of the expansion box, and may impact the overall speed of the computer system.
Therefore, it would be beneficial if that was a mechanism to provide an expansion box, especially for high speed expansion busses, which does not require the use of active circuitry.